Found in the last week or two...
Tomb Raider Chronicles
Ridge Racer Type 4
Tekken 3
Soviet Strike
PotC: the Legend of Jack Sparrow
Gottlieb Pinball Classics
Viewtiful Joe
Scrabble
All 50p each
Battle Construction Vehicles
Billy Hatcher and the Giant Egg
Metal Arms: Glitch in the System
£2 each
Inter-Act Superpad for GC £1
Got this for 1 Euro at a local market. Filthy as hell and I was sure it wouldn't work. To my surprise it works great.
Today I picked up a "broken" DMG Gameboy and loose carts of Tetris DX and Super Mario Land for 5 euros. I got it for the Mario Game itself which I didn't have and I thought that I can use the GB for a spare battery cover and parts.
I tried the GB and it wouldn't boot games but would show a corrupted Nintendo logo. Which I know is a sign of a dirty cart slot. (You dirty little slot...)
I opened it up, cleaned the connectors and now it boots up no problem. It has lines of dead pixels but that is easy to fix with a soldering iron.
So I scored a working (but yellowed) DMG with 2 great games for 5 euros. Not bad.